1. Field of the Invention:
This invention relates to a duplex copying mechanism.
2. Prior Art:
The conventional copying apparatus designed to copy both sides of a copy sheet is disclosed, for example, in U.S. Pat. No. 4,098,551 (Komori et al., patented July 4, 1978), in which an intermediate tray is disposed between upper and lower paper feed cassettes and a copied sheet discharge tray. Each copy paper sheet applied from a paper feed station to an image formation station and thereby having an image transferred thereon is stored in layers in the intermediate tray. The image-transferred copy paper sheets thus stacked in the intermediate tray are successively sent to the image formation station again, and then the paper sheets each have the underside thereof copied to finish duplex copying.
In the apparatus of the type described above, since the intermediate tray for copying both sides of copy sheets has to be disposed between the paper feed cassette disposed in upper and lower positions and the copied sheet discharge tray, the copying apparatus is enlarged in size. On the other hand, in the intermediate tray are the orderly stored copy sheets having the upper side thereof copied and on which electrostatic attraction due to corona charge produced in the step of transferring an image on one side of the copy paper sheet is liable to be retained. Because of this fact, it is difficult to feed one by one those copy sheets having one side copied in order to copy the other side because the paper sheets are electrostatically attracted to each other while the paper sheets are orderly stacked without getting out of place.
It is also difficult to deal one after another with copy paper sheets supplied in sheets stacked one over another and there is a possibility of the sheets having one side thereof copied being supplied at a time in several sheets to copy the underside of the copied sheet. Moreover, when each copy sheet having one side thereof copied and stacked in the intermediate tray is delivered one after another by sheet feed rollers, the copying apparatus often becomes stained with a copied image by the apparatus being pressed into contact with the sheet feed rollers and being pushed with respect to the copy sheet.
Conventionally, in the duplex copying apparatus, a duplex copying mechanism was incorporated into the main body of the copying apparatus, and accordingly, a user had to buy an expensive large-size apparatus whether or not it was intended to make both side copying at the time the duplex copying apparatus was purchased.
In another prior art apparatus the sheet velocity decreases as the sheet is transferred from a pair of drive rollers to the conveyor so as to provide a suitable slowing of velocity for laying the sheet, as for example described in the U.S. Pat. No. 3,942,786 (Unto Antero Lauren, patented Mar. 9, 1976). Such sheet laying means, however, provides for a sheet pile device.